I am on Lucid at about beta 2 version based on today's updates.
There is a serious error in the file mount on this version. I have been
trying sudo mount -o ro,loop filename.iso /mnt and the mount statement
gives a standard error which is a laundry list of mount commands. I
have seen this many times whan using sudo mount -t ext3 /dev/sda5 /mnt
and get the same error.

Does anyone else have this problem? If so I will put in a bug report.

sudo mkdir /mnt/iso
sudo mount -o loop filename.iso /mnt/iso

md5sum filename.iso and make sure the iso is good... a bad iso will
throw those "invalid filesystems" errors too. get the checksum and
compare it to the sum posted where you got the iso from.